In sputter ion pumps a glow discharge produces positive ions which are accelerated by an electric field and bombard or react with a cathode structure to sputter off cathode particles. The sputtered particles condense on other surfaces of the cathode, anode or other surfaces of the ion pump. The condensed cathode material entraps ions through the various entrapment mechanisms; as a result pressure within the pump is reduced. The entrapment mechanisms include: 1. Chemical combination for chemically active gases such as oxygen and nitrogen; 2. Burial and diffusion for small gas molecules such as hydrogen and helium; 3. Burial and covering over with further sputtered deposits. The ion covering or capturing mechanism is particularly suitable for pumping noble gasses such as argon, neon, krypton and the like.
The structure and operation of sputter ion pumps is well known. U.S. Pat. No. 2,993,638 relates to an ion pump in which the sputtering is enhanced by employing closely spaced louvers which are disposed at grazing or glancing angles with respect to the incident impinging ions. U.S. Pat. No. 3,319,875 discloses a sputter cathode composed of a number of concentrically disposed frusto-conical members of increasing radius opposite and coaxial with cylindrical anodes. U.S. Pat. No. 3,091,717 discloses a sputter cathode grid formed by affixing one or more spiral tapes onto a cathode plate as, for example, by spot welding or brazing. A plug is disposed at the center of the spiral cathode for providing sputter particles at the intense region of the glow discharge, thereby increasing the life of the cathode structure. U.S. Pat. No. 4,631,002 discloses a sputter ion pump which includes a plurality of cylindrical hollow anode cells arranged between two cathodes. The cathodes are formed with inwardly extending blades arranged radially adjacent each of the anode cells, and provide an increased sputter surface. In addition, the construction is such that the cathodes can be easily manufactured by punching and the like.
Two electrical configurations of sputter-ion pumps are disclosed in these patents. One, the "diode" configuration, applies positive high voltage to the anode structure and maintains the cathode plates at ground potential. The other, the "triode" configuration, applies a negative high voltage to the cathode plates and maintains the anode structure at ground potential.
It is desirable to provide cathode structures which have large sputtering areas; which are arranged for grazing incidence of ions for high sputtering rates; which generate substantial areas shadowed from sputtering, which are useful in both "diode" and "triode" configurations and are easy and inexpensive to fabricate.